General methods for dealing with graffiti fall into on of three categories: removal by an abrasive method (such as sandblasting), chemical removal, or repainting over the graffiti. These methods are described in detail by Leys in U.S. Pat. No. 5,346,640. As noted in the patent, each method has its disadvantages in terms of cost, labor and environmental impact. Leys, the disclosure of which is incorporated herein by reference, proposes to provide graffiti removers based on N-methyl-2-pyrrolidone, propylene carbonate, isocetyl alcohol, a glycol ether ester, a surfactant and a thickener. The reference teaches that permanent marker inks, as well as spray paints can be removed, and mentions that, in some of the above listed, dimethyl sulfoxide in an amount of between about 10 and about 30 percent is useful to help remove heavy old graffiti and underlying paint from all surfaces except plastic.
Pourreau, U.S. Pat. No. 5,712,234, describes graffiti removers particularly useful for removing permanent ink from painted surfaces which include a dye solvent (a pyrrolidine or lactone), a dye non-solvent (a glycol ether ester or a glycol diether), and a dye bleaching agent. It is mentioned in this reference that the dye bleaching agent (which comprise difficult to handle oxidizing agents, reducing agents and bases) are keys to success, and further that optional components that can be included comprise thickeners, surfactants and the like. Specifically mentioned is the use of water in a final step to remove both graffiti and the cleaner composition from the painted surface.
Jackson, U.S. Pat. No. 4,780,235, describes a low toxicity paint remover composition containing C.sub.1 to C.sub.4 dialkyl esters of C.sub.4 to C.sub.6 aliphatic dibasic acid, an activator, a thickener, a surfactant and at least one other organic nonhalogen-containing solvent. It is mentioned in this reference that the activator is a key ingredient and typically is a difficult-to-handle-base (ammonium hydroxide or monoethanolamine) or -acid (formic acid, acetic acid or oxalic acid), some of which smell badly and some of which are toxic. None of the nonhalogen-containing solvents specifically mentioned include sulfones and sulfoxides, especially not mentioned is dimethyl sulfoxide. Among the thickeners specifically mentioned are effective amounts, in general, between about 0.5 and 10 wt. % of ethylcellulose, hydroxypropyl cellulose, organic modified clay and hydrogenated castor oil.
Still needed in the art are graffiti removers that will effectively remove stains of an organic nature, especially permanent inks and dyes from painted surfaces without harming the underlying surfaces, without using harsh chemicals as activators and/or dye bleaching agents, which operate slowly, allowing a more concentrated attack, but efficiently, even on vertical surfaces, and which are cleanable by rinsing with water.
The present invention is based on the discovery that if a suitable filler is used in combination with an active solvent and a secondary solvent, graffiti removers can be developed which are efficient to remove stains that are organic in nature from a variety of surfaces employing very mild solvents in compositions that are relatively environmentally friendly when compared to those which are now known in the art. While not intending to be bound by any theory of action, the filler appears to hinder solvent evaporation into the air, thus allowing it to fully attack the graffiti or stain, and without the side effect of destroying most of the surfaces on which it is applied.